Removing the blue tractor parking brake valve.

[Full Floater]

Im in the process of tiding up a bunch of hack job air line repairs and routing on a 75 R model.    What are you thoughts on removing/bypassing the blue tractor parking brake valve, leaving only the yellow and red, as in more modern applications.   The tractor is a straight truck and will never be pulling a trailer, so no real need to keep the trailer charged and the tractor brakes set for any reason, thus not needing the blue valve....unless it has a use that I'm not familiar with....

 

Just wanting to simplify things and keep the "what is the blue knob for" conversations to min with future drivers.

 

Thanks folks.

[67RModel]

Might not be a bad idea given the fact you will never need it for any purpose. I have never had the dash apart in something with a blue valve. Is the valve all one unit with the red and yellow or is off by itself? If your back there gutting out unused stuff and cleaning up poor repairs and workmanship it might be worth it to just get rid of all the old valves and throw a new parking brake valve (yellow button) in it so you know it pops off at 60psi and be done with it. Sounds like you are going to have drivers in it and be using it for actual work. In this case you want everything to be in good condition and as basic as possible.....

[Full Floater]

Yes the blue one is independent of the yellow and red valves.  There is a line from the yellow, going to the blue....not sure what it is, but im going to try to delete it.

Simple is good.   

[mechohaulic]

for what ever reason the blue was the "one valve "does it all idea.  possibly like other brain dead ideas (121 brakes and others) . drivers may have only pulled the yellow =not the red and accidents happened ? feed for brakes should have gone to blue then yellow / red. simple is better. 

[67RModel]

I’ve only driven a few trucks with the blue button and never used it. I was always told its only practical purpose was so you could set the tractor brakes only and go back and adjust the trailer brakes without having to release everything and chock the wheels. I don’t know if there were others uses for them or not….

[Geoff Weeks]

As with others, I have little experience with them, drove a R model that had the blue knob.

 Some (I know some Fords) had the red, yellow, blue as part of one big multi function valve, so if yours is that way, it will be hard to remove just the blue.

Most trucks, you can push the red button in and release the trailer brakes with the yellow (tractor parking button out) and it will stay in. I have heard of some that will not, and I think those are with the blue button.

On most trucks, if you pull the yellow with the red in, it will trip the red as well. It depends on how the trip is plumbed.

 So, in short, try and push the red in (with the red hose deadheaded) with the yellow out, If you can and it locks in, I'd say go for it. If however the red can't be locked in without the yellow in, I would leave it as is.

I really don't see a reason to mess with it,

 

[doubleclutchinweasel]

You only need the blue valve to set the tractor brakes and leave the trailer brakes free to roll. Is kinda important with the roll-back type trailers. The Landoll Haul-all trailers need this setup. Other than that, not really much need for it. 

Edited August 8, 2023 by doubleclutchinweasel

[Geoff Weeks]

All my stuff can do it with just two buttons. Bendix MV-2, I've talked to some guys that can't keep the red in with yellow out, I think those systems used the Blue button. Not why they were that way. All had to due with how the red button "tripped" when parking brake was pulled.

 Assembling multi-piece heavy haul trailers it can come in handy to winch against the tractor with the trailer supplied with air.

[doubleclutchinweasel]

I’ve driven Mack’s with 2 different “red” buttons. On some, the red would stay in even when the yellow was pulled. On others, the red would pop out when the yellow was pulled. 
 

Difference is one was spring loaded and the other was not.  

[doubleclutchinweasel]

Oh, on both of those, the yellow button still applied tractor and trailer brakes when pulled. The yellow “system” button was first in line. So, when it was pulled, it dumped air out of both systems and applied the brakes. 

The only difference was whether or not you had to push the red trailer brake valve in after you pushed the yellow button in. 

[Geoff Weeks]

It sound more like the one with the red button in was pre -121.  One of the requirement -121 brought in that wasn't there before, was the tractor feed to pop-out when the parking brakes were applied. Prior to this, the tractor protection valve is what cut off the pressure to the trailer lines based on pressure on a small control line from the dash control. TP 1 or TP2. With this system, the control on the dash could be left in the trailer position and it wouldn't supply air until the truck pressure was between 30 and 40 psi. The problem was if the driver left it in the (normal, supply trailer air) on shut down, it would, on start up release the trailer brakes without input from the driver.

 With -121 the trip mechanism was moved from the TP to the control valve on the dash.  Until -121 reservoir air pressure was supplied to the TP at all times, the small control line opened the TP (and allowed supply and control brake air to the trailer). Post 121 the air supply line goes through the dash control to the TP. Until the dash valve supplys air to the TP it stays closed, All air to the red line, passes through the dash control. Until recently, only 4 lines were used on post 121 TP valves two input and two out to the trailer ports. (TP-3).

 This was all to prevent a driver from going to a combo in the yard that the previous driver had left the trailer controls in the "normal" position, the new driver fireing up the truck and assuming the trailer brakes were set, having them release as pressure builds.

 The post -121 requires that on pressure loss the TP and controls self return to the closed position without any input from the driver.

 The valve assemblies like the MV-2 or -3 all do this but allow the red button to be pushed and supply air while the tractor brakes remain set. The requirement is, if the tractor parking (yellow) is pulled, it must trip the red automatically. The is no requirement that the trailer can't be supplied air when the tractor brakes are set. 

 There are more than one way to achieve the requirements,  Some chose one way, others chose another. In the end the most common way had the fewest knobs/valves.

Edited August 8, 2023 by Geoff Weeks

[doubleclutchinweasel]

Yes, Geoff. One was older. One of the ones where the red button stayed in was a ‘67. The last one I had,  where the red button popped with the yellow button, was a ‘70. 

Not sure how that aligns with the new regulations.  Not sure if those setups were factory on both or not.

I only drove 1 truck that had all 3 buttons.  It was a Peterbilt.  I can't remember for sure if the blue, tractor brake button popped out when the yellow was applied.  But, I don't THINIK it did.  But I can't remember that for certain either way.

Funny how the older the memory, the clearer.

Edited August 8, 2023 by doubleclutchinweasel

[Geoff Weeks]

24 minutes ago, doubleclutchinweasel said:

 

 

 

Funny how the older the memory, the clearer.

1st sign of old age, and I can't remember the 2nd!

Yeah, '67 is Pre-121. My '69 was also. Not sure when -121 took over completely, my '73 still has the "slippery road"  manual push-pull valve on the dash to cut the front brake pressure. '69 had cable operated valves (like the flippers on the dash for PDL but with cable handles) down under the dash for trailer supply and slippery road limiting valve. Other than that, the '73 is all post -121 on the brake set-up.

'69 had a pop-out button for parking/E brake and a TP-2 for tractor protection. I just used it as a yard goat,  Weird haveing the trailer valve operated by the same cable/knobs as were used to control the heater and vents. Don't reach for the wrong one, or you'll regret it.

'69 cab is on the back of my '42 this morning, going to make a run to the recycle yard today. Cab was all rotted out. Got aa bunch of Firestone RH 5 deg semi-drops to go with it for scrap. Funny the '69 frame is in near perfect condition. Body was totally rusted. Sold the engine out of it for what I paid for the truck, Couldn't give away the 5 speed Clark, the rear was re-ratioed and went into my Marmon, Hood went on my '73. I guess I got my $350 out of that truck!  It had a 406 gasser in it. Both fuel tanks went on my '42

[doubleclutchinweasel]

24 minutes ago, Geoff Weeks said:

1st sign of old age, and I can't remember the 2nd!

No kidding!

[Full Floater]

Got er done.   Removed this and that, the valve is gone, more space to see what's going on behind the dash....the yellow and red still work as they are supposed to. Replaced a few air lines. Nothing's leaking.  Im happy.    

Thanks folks.